1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic storage apparatus.
2. Description of the Related Art
Applications of the magnetic storage apparatus such as an HDD (Hard Disk Drive) are increasing, and importance of the magnetic storage apparatus is increasing. In addition, in the magnetic recording medium such as a magnetic disk, the recording density is increasing at a rate of over 50% per year, and this trend may be expected to continue in the future. With this trend of increasing recording density, magnetic heads and magnetic recording media suited for the high recording density are being developed.
The magnetic storage apparatus may be provided with the so-called perpendicular magnetic recording medium in which an axis of easy magnetization within a recording layer is mainly oriented in a perpendicular direction. In the perpendicular magnetic recording medium, the effects of demagnetization is small in a boundary region between recorded bits, and a sharp bit boundary may be formed, to thereby suppress increase of noise, even when the recording density is high. In addition, in the perpendicular magnetic recording medium, the decrease in the recording bit volume caused by the high recording density is small, and the thermal stability of written bits (or characteristic to withstand heat fluctuation) may be improved. The thermal stability of written bits may also be simply referred to as “thermal stability”.
In order to cope with the demands to further improve the high recording density of the magnetic recording medium, studies are being made to use a single-pole head having a desirable write performance with respect to the perpendicular recording layer. More particularly, a proposed magnetic recording medium is provided with a back layer made of a soft magnetic material between the perpendicular recording layer and a nonmagnetic substrate, in order to improve the input and output efficiency of magnetic flux between the single-pole magnetic head and the magnetic recording medium.
Further, in order to improve the recording and reproducing characteristic and the thermal stability of the perpendicular magnetic recording medium, so as to carry out high-density information recording and reproduction, a Japanese Laid-Open Patent Publication No. 2004-310910 proposes forming a perpendicular recording layer by two or more magnetic layers, for example. One magnetic layer includes Co as a main component, and further includes Pt and an oxide. The other magnetic layer includes Co as the main component, and further includes Cr but no oxide.
However, in the conventional magnetic recording medium and the conventional magnetic storage apparatus, it may be difficult to simultaneously improve the recording capacity and the recording and reproducing characteristic.